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Thread: Active Loudspeakers - The what, where, why and how of your active loudspeaker project

  1. #16
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    Can the above situation be improved?

    Someone says yes. Put in a charge coupled passive crossover. Another says put in updated drivers and an updated passive crossover.

    This will improve the refinement of the system but it won’t fix the underlying issues holding back the system.

    In my practice of looking at these systems in use l evaluate the actual operating conditions.

    Typically such a system is used in a small room at a distance of 2.5-3.00 metres at a typical loudness of 93 db spl from each loudspeaker.

    The power amplifiers are two stereo K1 Crown power amplifiers purchased off EBay. They are rated at 350 watts rms into 8 ohms per channel. The amplifier gain is 31.55 db ref 1.4 volts input signal. SNR 100 db below rated power.
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  2. #17
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    JBL 5234A Electronic Frequency Dividing Network

    https://jblpro.com/en/site_elements/5234a-information
    Referring to the attached spec screen shot the rated output is 6.2 volts @ +18 db ref 0.775 volts
    The SNR is -90 db ref the rated output.
    Inputs are balanced
    Outputs are unbalanced and requires floating balanced transformers for balanced operation to fully utilise balanced inputs to a power amp as noted in the user manual

    https://www.manualslib.com/manual/10...?page=6#manual

    The preamp is a hifi unit made by Adcom
    Specifications ; Total harmonic distortion · 0.003% ; Signal to noise ratio · 90dB (MM), 100dB (line) ; Output · 2V (Pre out) ; Dimensions · 432 x 289 x 76mm ; Weight ...
    Signal to noise ratio: 90dB (MM), 100dB (line)

  3. #18
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    SNR analysis

    Now l will analyse the typical operating conditions stated above and relate that to the specifications of each of the power amp, the active crossover and the preamplifier.

    Firstly l need to establish the loudspeaker operational conditions

    A rudimentary bit of Mr Spock’s Vulcan maths indicates the 4343 loudspeaker requires approximately 8 watts of power to produce an spl of 93 db at 2.5 - 3.00 metres. This equates to 8 volts rms at the output of the power amplifier.

    Spl drops for each doubling of distance from
    The source.

  4. #19
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    Looking at the power amplifier

    The input signal voltage required by the Crown power amplifier is 0.211 volts for an output of 8 volts rms. Noted this power amp has a relatively high gain of 31.55 db ref an input sensitivity of 1.4 volts. The SNR is -100 db. Given the operational signal level is -16.4 db below the 1.4 volts for the rated power output the SNR at this input level is -83.57 db.

    That’s not really an acceptable SNR for a recorded music monitoring system. A preferred SNR at the rated output is -110 to -118 as specified in some Macintosh power amplifiers and Bryston power amplifiers.

    My suggestion is to use a power amplifier with a voltage gain of 26 db rated at 200-250 watts rms with a SNR of - 110 to -118 db. The input sensitivity will be 2.24 volts for the rated output. It’s unlikely you will ever operate the power amplifier at full output.

    Most preamplifiers will easily provide this maximum level before clipping of the pre amplifier.

    The SNR at the 0.211 signal level will be the -118fb of the power amplifier + 20db = 98db. That’s a significant improvement over the Crown power amplifier.

  5. #20
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    Looking at the active crossover

    Moving on the the active crossover with the line signal level of 0.211 volts the SNR of -90 will now be reduce by 29.36 to - 60.64 db.

    That’s not acceptable.

    It’s best to aim for an active crossover with a SNR of -100 db or better ref to an input sensitivity of 1.4 volts.

  6. #21
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    Looking at the preamp

    Looking at the preamp it’s rated SNR of -100 db at 2 volts will reduce by 19.5 db to -80.47 at a line signal level of 0.211 volts. That’s only marginally acceptable. Aim for a preamplifier with a SNR of -110 at 1.4 volts.

    Looking at the above adjusted SNR figures you can see the active crossover has the worse SNR of all the components in the signal path.

  7. #22
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    But we’re not done.

    Each component has a residual noise component. That is compared to the SNR at the rated output. Manufacturers dislike quoting the residual noise for that reason.

    At the power amplifier output these residual noise frequency figures sum. Obviously this summed residual noise has to be compared the the output voltage of the power amplifiers.


    Using some more of Mr Spock’s Vulcan maths l have calculated the total residual noise at
    0.00022 volts.

    This equates to an overall SNR of - 59.48 db referred to the 0.211 line signal level.

  8. #23
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    If someone quoted at the SNR of an audio component you wouldn’t buy it.

    I checked these figures against the power amp output voltage for 8 watts mentioned above.

    Referring to the 8 volts required for 8 watts and the 93 db listening level at 2.5 to 3.00 metres the total summed residual noise is -60 below the 93 db level.

    So the effective system noise floor is 33 db spl at the listen position!

  9. #24
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    The dynamic range of human hearing is 120 db. Therefore this residual noise will be audible. More so on some program material.

    A vinyl record has a dynamic range of 70 db and a CD has a dynamic range of 90 to 93 db.

    What it means is this SNR is above the noise floor of both program sources. So this is real problem if your aim is to fully appreciate the dynamic range of your 4343 system.

    This noise will also completely shroud any likely total harmonic distortion.

    I have not discussed the potential of earth - ground loops yet which can be only -20 db below the signal level.

    The question is how do you improve on that residual noise performance?

  10. #25
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    An active crossover with a rated SNR of -100 db ref 1.4 volts rate output will improve the overall system SNR to - 72.86 db at the 8 watt loudspeaker output level to an spl of 20.14 db. At this power level the signal spl from the loudspeaker is 93 db at 2.5 to 3 metres

    That’s an improvement of 13.3 db. So the residual noise will be around half as loud.

    But you still have an audible noise level of 20 db at the listening position. It’s only just below the dynamic range of a vinyl record. So if you think a vinyl record is noisy between tracks this is a -70 db level!

    To be effective the noise level of the signal path should be at least -20 db below the dynamic range of sources.

    Ideally the residual noise level should be approaching-100 db below a given signal level. Not just the rated output.

    You might when might wonder why a demonstration of a premium hifi system was so resolving and overall impressive. The dynamic range under real operating conditions a big part of it. Not the quoted SNR at the rated output level of a component.

    Dynamic range is not about how loud your system can go. It’s actually about how quiet it is under normal operating conditions.

    A really well designed piece of equipment shouldn’t need to be played loud to hear everything in the recording. Thats what are you pay for. A linear and accurate monitor loudspeaker requires audio electronics with a noise floor well below the dynamic range of the program source at normal listening levels to identify all the information on the recording.

  11. #26
    Senior Member 1audiohack's Avatar
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    Nice work Ian.

    Possibly how a rank amateur would configure a system, as improperly as possible. Even leaving the excess gain amp argument alone the system described is:

    Every output single ended.

    Every input differential drive.

    All the gain at the end of the signal chain.

    Every rule of signal chain gain stage broken.

    Poor SNR will undoubtedly be but one of the results.

    What would be the results if we fixed all the above?

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

  12. #27
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    Quote Originally Posted by 1audiohack View Post
    Nice work Ian.

    Possibly how a rank amateur would configure a system, as improperly as possible. Even leaving the excess gain amp argument alone the system described is:

    Every output single ended.

    Every input differential drive.

    All the gain at the end of the signal chain.

    Every rule of signal chain gain stage broken.

    Poor SNR will undoubtedly be but one of the results.

    What would be the results if we fixed all the above?

    Barry.
    -96.6 db SNR at the 1.4 volt signal level. Add +16 db of noise at the listening levels l referred to above. That assumes blameless equivalent.

    There are ways of improving on the noise level up to 20 db when bi amping at real (normal levels). This will feature in my forthcoming analogue active crossover using some elaborate technology.

    Edit. It took a long time find and understand the problem. Fixing the problem was about technology and good design. I mean why come out with something what isn’t a real improvement on the current state?

  13. #28
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    The other way around this is it sit 8-10 metres back from your system and just use more power.

    But that’s not doing to work for most users in a domestic situation.

  14. #29
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    Hello Ian

    I think you are forgetting something. All rooms have residual background noise. If I understand you correctly you are saying the noise at some fixed gain setting is 33 Db in level and because we can hear from 0-120 it will be audible. That is way over simplified. You may not hear it at all depending on frequency content and the rooms own background level. Typical rooms have between 40-50 DB of noise at all times.

    Rob
    "I could be arguing in my spare time"

  15. #30
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    Quote Originally Posted by Robh3606 View Post
    Hello Ian

    I think you are forgetting something. All rooms have residual background noise. If I understand you correctly you are saying the noise at some fixed gain setting is 33 Db in level and because we can hear from 0-120 it will be audible. That is way over simplified. You may not hear it at all depending on frequency content and the rooms own background level. Typical rooms have between 40-50 DB of noise at all times.

    Rob
    Yes l was having a seniors moment… Lol.

    The cone of silence 🤐.

    I’m not here to sell anything.

    I think you make an observation but there are numerous variables that require expertise well beyond the realms of this thread. For example when you quoted that measurement what was the actual source of the noise? Without that your statement is meaningless.

    The more you know the more you need to know … Lol 😂.

    https://en.m.wikipedia.org/wiki/Hearing_range

    There’s deep complexity on the subject of human hearing.

    Why and under what circumstances is the human ear able to discriminate certain types of sounds ???

    Why can people hear silent vinyl recording groove? Referring to the quote below.

    The real misnomer is in fact what your ears focus in on and how it effects the listening experience.

    “Vinyl records have a typical dynamic range of around 70 dB, depending on the equipment used to record the audio and cut the record. CDs have a typical dynamic range of 90 to 93 dB, though 16-bit digital audio has a theoretical dynamic “

    They can also hear the hiss of the moving coil preamp when the stylus is lifted off the record which is at next -75 db referred to a given level like 0.5 mv. It’s virtually impossible to make it quieter.

    Why can a woman detect even the quietest fart in a busy shopping mall??? Because they are attuned to that aggregating sound. This has been the subject of numerous marital issues…Lol.

    In my own experience those noises detected in a random spl measurements by an un trained person are often in a particular frequency band and a particular source. I happen to know this because l did some product research into sound proof glass. There are actually different classes glass noise reduction depending on type and source of sound on the exterior of a property and the particular occupation in a commercial dwelling.

    It’s not simple. It’s actually a science. Let’s leave it there
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